Abstract:Microalgae releases extracellular substances around the cell to form a unique algal microenvironment called "phycosphere niche" that attracts a large number of bacteria to colonize. The algae-bacteria interactions are very complex involving multiply material exchanges and information communication. Among the algae-bacterial relationship, extracellular polymeric substances (EPS) serve as a bridge for matter flux. Both microalgae and bacteria can produce EPS, and the production process is regulated by many factors. In the phycosphere environment, EPS play important ecological roles, such as participating in the formation of biofilm, affecting the algae-bacterial symbiotic structure and regulating the composition of microbial communities. In addition, as an important member of EPS, transparent exopolymer particles (TEP) mediate the conversion of dissolved organic carbon into particulate organic carbon. This profile made TEP is an important regulator, participating in marine carbon cycle. In this review, we focus on phycosphere niche, and summarise the newest advance in EPS production, composition and effect factors. Meanwhile, the ecological roles of EPS in marine carbon cycle have also been discussed, to provide reference for better understanding the organic matter properties and algae-bacterial behavior in the phycosphere environment.

Abstract:Diarrhea Escherichia coli is one of the main pathogens causing human and animal diseases in the world, and brings great losses to the social economy. According to different pathogenic mechanisms, diarrhea Escherichia coli can be divided into six types:enteropathogenic E. coli, enterohemorrhagic E. coli, enteragglutinative E. coli, enterotoxigenic E. coli, diffusion adhesive E. coli and enteroinvasive E. coli. Different pathogenic E. coli invades the host in different ways and causes different inflammatory reactions. In this paper, the differences of inflammatory signal pathways caused by different pathogenic E. coli were analyzed, and the relationship between inflammatory signal pathways and pathogenic infection, prevention and treatment were discussed. The paper aims to lay a foundation for the study of pathogenic mechanism and treatment of diarrhea E. coli.

Abstract:Ectoine and its derivative 5-hydroxyectoine (5-HE) are compatible solutes synthesized intracellularly by halophiles in response to high salinity/osmolarity, heat, freezing, and dryness extremes. They have drawn a lot of attention lately due to their protective effects on maintaining cell survival, membrane integrity, as well as protein and DNA functionality. This article comprehensively reviews the regulatory mechanisms of intracellular biosynthesis and catabolism of ectoine and 5-HE in different types of microorganisms, and summarizes the latest research progress in the regulation of extracellular uptake and transport systems of ectoine and 5-HE. This review may provide a certain theoretical reference for the subsequent optimization of the production and efficient accumulating strategies of ectoine and 5-HE.

Abstract:Vibrio parahaemolyticus is a widely distributed foodborne pathogen in seafood, often leading to diseases in aquaculture animals or food poisoning for human beings. Thermotolerant direct hemolysin (TDH) is one of the most important virulence factors of V. parahaemolyticus. This article systematically reviews the widespread distribution, spreading, the diversity and expression regulation of tdh gene, as well as the structure, biological activity and promising research directions of TDH protein. The article aims to deeply understand the symptoms caused by V. parahaemolyticus infection, and hence to provide theoretical support for the prevention and clinical treatment of V. parahaemolyticus infection.

Abstract:Currently, it is widely accepted that the combination of advanced synthetic biology techniques with traditional molecular genetic techniques could help construct and optimize metabolic pathways in yeast cell factories. The research of yeast synthetic biology first began in the model yeast Saccharomyces cerevisiae, and in recent years has rapidly expanded to some unconventional yeast species including Pichia pastoris, Yarrowia lipolytica, Kluyveromyces lactis, and Hansenula polymorpha. By using synthetic biology-based metabolic engineering strategies, scientists have successfully developed a series of unconventional yeast cell factories that can efficiently produce different valuable industrial products such as biomaterials, biofuels, biochemicals, enzymes, food additives and pharmaceuticals. This review systematically summarizes the current status and applications of synthetic biology tools (mainly genome editing tools), synthetic biological parts (mainly promoters and terminators) and related molecular genetic methods in the aforementioned unconventional yeast systems. Furthermore, potential applications of other synthetic biology approaches in further optimizing bioproduction in the unconventional yeast biofactories and key challenges are discussed. This review provides a theoretical guidance for engineering these promising non-model microbial chassis to achieve high-level production of value-added products.

Abstract:[Objective] The objective of this study was to assess the effect of fermented cotton stalk in the diet on rumen microflora of weaned lambs by using high-throughput sequencing technology.[Methods] Thirty Hu sheep were selected and randomly divided into three groups according to different proportions of fermented cotton stalk in the diet:the control (S0), 50% fermented cotton stalk (S50) and 100% fermented cotton stalk (S100), six sheep were randomly slaughtered in each group to analyze their growth performance, rumen fermentation parameters and microflora analysis.[Results] Feeding 50% fermented cotton stalk can significantly improve the daily gain and slaughter rate of lambs (P<0.05). Bacteroidetes and Firmicutes are the dominant phylum in the rumen, Prevotella and Unclassified Bacteroidales are the dominant genus of the rumen of the lambs. Adding 100% fermented cotton stalk to the diet could significantly reduce both the diversity of rumen microflora and the relative abundance of Unclassified Bacteroides and BF311 (P<0.05). Three metabolic pathways significantly increased as the proportion of fermented cotton stalk increased (P<0.05).[Conclusion] Feeding 50% fermented cotton stalk had little effect on the structure and function of rumen microflora while increasing daily weight. In production practice, the content of fermented stalk should be lower than 50%.

Abstract:[Objective] Here, we explore the effect of the low concentration tetracycline (TC) and Benzo [a] pyrene (Bap) on the generation of high resistance gene tetA(C) mutations in the environment.[Methods] Escherichia coli, pACYC184 plasmid and tetracycline resistance gene tetA(C) was used as the host strain, the vector and the research object, respectively. Error-prone PCR was used to construct the gene library, the code table of high resistance mutation sites was established corresponding to high resistance mutants in the gene library. At the same time, the E. coli carrying pACYC184 were cultivated with 0-10 mg/L TC and 0-30 mg/L Bap 14 d. We randomly selected ten high resistance mutation from each group. The tetA(C) genes in these mutations were then sequenced. Sequencing results were compared with the code table of high resistance mutation sites, calculated the proportion of high resistance mutants caused by tetA(C) gene mutation in all high resistant strains.[Results] Sequencing results showed that under the selection pressure of low concentration TC, while the Bap concentration increases, the frequency of high resistance gene mutant increases (P ≤ 0.01). But without TC, there is no corelation between Bap concentration and the frequency of high resistance gene mutants (P>0.05).[Conclusion] When Bap and low concentration TC both in the environment, the high resistance mutants were easier survived by selection pressure.

Abstract:In prokaryotes, selenoprotein synthesis requires the interaction between selenocysteine (Sec)-specific tRNA^Sec (SelC) and selenocysteinyl tRNA synthase (SelA) or Sec-specific elongation factor (SelB).[Objective] Based on the Sec insertion machinery in Escherichia coli, we aimed at finding key sites of tRNA^Sec scaffold and providing a new way to solve the problems of low Sec insertion efficiency and low yield of selenoprotein.[Methods] We used rat cytoplasmic thioredoxin reductase (thioredoxin reductase 1, TrxR1) as a model selenoprotein. First, we constructed tRNA^Sec by site-directed mutagenesis, and transformed them to BL21 (DE3) gor-to obtain a positive recombinant strain (carrying pET-TRSter'/pSUABC), which was used to express rat cytoplasmic thioredoxin reductase 1 (TrxR1). Then TrxR1 was purified using 2',5'-ADP Sepharose affinity chromatography and gel filtration. The enzyme activities of TrxR1 were determined by the classical Se-dependent DTNB reduction assay to analyze the key nucleotide sites and evaluate the Sec incorporation efficiency.[Results] When tRNA^Sec co-expressed with SelA and SelB in the presence of the bacterial SECIS element, the activities of TrxR1 decreased at varying degrees compared with wild type. Among them, the enzyme activities of all G18 and G19 mutants were much lower than that of wild type (<10%). However, the enzymatic activities of a26 and b7 were relatively high.[Conclusion] G18 and G19 nucleotide sites of E. coli tRNA^Sec may play a vital role in maintaining the stability and flexibility of tRNA^Sec. Site-directed mutations of tRNA^Sec causing the conformational change may affect the interaction between tRNA^Sec and Sec elements. Thus, it is possible to improve the Sec insertion efficiency via proper modification on tRNA nucleotide sites.

Abstract:[Objective] Meloidogyne incongnita is a soil transmission plant parasitic nematode that causes serious losses to agricultural production worldwide. Panebacillus polymyxa KM2501-1 inhibits Meloidogyne incongnita in greenhouse experiment, and could produce a variety of nematocidal volatile organic compounds. But whether its non-volatile products have nematocidal activity is still unknown. This study focused on identification of non-volatile nematocidal metabolites from Panebacillus polymyxa KM2501-1.[Methods] Strain KM2501-1 was fermented to collect supernatant. The high purity nematocidal substance was isolated and purified by silica gel column chromatography and high-performance liquid chromatography. The structure of the nematocidal substance was identified by liquid chromatography-mass spectrometry and nuclear magnetic resonance.[Results] The fermentation filtrate of Panebacillus polymyxa KM2501-1 inhibited Meloidogyne incongnita and the egg hatching of Meloidogyne incongnita. The nematocidal efficiency was 87.66% in vitro and the egg hatching inhibitory efficiency was 92.26%. The results of structural identification showed that the nematocidal active substance produced by Panebacillus polymyxa KM2501-1 was cyclo (Pro-Phe). The nematocidal efficiency of 800 mg/L cyclo (Pro-Phe) was up to 84.75% after 96 hours exposure. Microscopic observations show that the intestinal tissue of the Meloidogyne incongnita treated with the cyclo (Pro-Phe) was disordered compared with the control group.[Conclusion] The cyclo (Pro-Phe) produced by Panebacillus polymyxa KM2501-1 is a new nematocidal substance that may inhibit nematodes by destroying the nematode intestinal tract.

Abstract:[Objective] This study aimed to isolate and screen bacterial endophytes with potential plant growth-promoting activities from Astragali Radix, and to explore effects of green leaf volatiles (GLVs) on the endophytes.[Methods] Plate culture method was used to isolate bacterial endophytes from the root tissue of 7-year old plants of A. mongholicus in Hunyuan, Shanxi, China and 16S rRNA gene sequencing was used to identify the isolates. The screening for plant growth-promoting endophytes was performed by adding exogenous 1-aminocycline-1-carboxylic acid (ACC), tryptophan, calcium phosphate and feldspar into the medium and by incubation in the medium lacking nitrogen source, further quantification was carried out by inductively coupled plasma mass spectrometry (ICP-MS) and spectrophotometry. Effect of the main GLVs in Astragali Radix on the isolates was investigated by adding synthetic chemicals into the liquid medium and the ten isolates containing ACC deaminase were used as representative strains. Headspace GC-MS was performed to determine the contents of the main GLVs in Astragali Radix.[Results] A total of 85 bacterial strains were obtained and classified into the follow phyla:Proteobacteria, Firmicutes, actinobacteria and Bacteroides. At the genus level, they were categorized into 13 genera and the stains of Pseudomonas, Pantoea and Staphylococcus were more abundant (80.00%) than the ones of the others. Among candidate plant growth-promoting isolates, these that can synthesize indoleacetic acid (IAA) shared the biggest proportion (69.41%), followed by these with ACC deaminase (40.00%) and nitrogen fixation activity (31.76%), and these that can solubilize phosphorus and potassium shared relatively lower proportions (i.e., 14.12% and 7.06%). Among the isolates with double plant growth-promoting activities, the IAA-producing strains containing ACC deaminase shared the biggest proportion (37.65%), followed by the IAA-producing strains with nitrogen fixation activity and the strains with ACC deaminase and nitrogen fixation activity, accounting for 28.24% and 24.71%, respectively, while these that not only contain ACC deaminase but can solubilize potassium bearing minerals shared the smallest part (1.18%). Besides, low concentrations of GLVs (i.e., 2-50 μmol/L of hexanal and Z-3-hexenal, and 5-125 μmol/L hexanol) exerted positive effects on the growth of a few strains with ACC deaminase.[Conclusion] There were bigger proportions of the isolates that can produce IAA and/or contain ACC deaminase and GLV growth-promoting strains in the bacterial community residing the root tissue of A. mongholicus in Hunyuan, which might be resulted from the local adaptation. GLVs might be involved in the shaping of the composition and function of endophytic communities in Astragali Radix in Hunyuan.

Abstract:[Objective] The purposed of this study is to obtain some microalgae with fast growth and high oil producing ability. In addition, the effects of different culture methods on microalgae growth characteristics such as biomass, oil producing capacity and carbon consumption, and the adaptation of strains to pH were studied.[Methods] The method of phosphoric acid-vanillin reaction and Nile Red staining was used for obtaining some oleaginous microalgae. At the same time, different culture methods such as photoautotrophy, heterotrophy and mixotrophy, were studied by using GC-MS technique.[Results] Two strains of H and Z₈, which could produce 1.14±0.05 g/L and 1.33±0.10 g/L total lipid, respectively, were obtained. According to the results of morphological observations and 18S rDNA analysis, strains H and Z₈ had the highest homology with Chlorolobion braunii and Desmodesmus intermedius, so the strains were identified as Chlorolobion braunii H and Desmodesmus intermedius Z₈. Furthermore, H and Z₈ belonged to the growth coupling type based on the results of the kinetic model. There was no significant difference in the total lipid and biomass between H and Z₈ when the pH value was between 6.0 and 9.0 (P<0.05). The percentage of C16 and C18 fatty acids in total fatty acid from the strains H and Z₈ was more than 90%. The biomass from mixotrophy was better than heterotrophy, but it was more conducive to lipid accumulation under heterotrophic conditions. Furthermore, the strains of H and Z₈ have a wide pH adaptability.[Conclusion] These results indicate that the two strains are excellent potential lipid-producing strains.

Abstract:[Objective] The objective of this trial is to investigate the quality variation and the accumulation of deoxynivalenol and 15-acetyldeoxynivalenol in corn with different Fusarium graminearum inoculation under aerobic conditions.[Methods] Single factor experiment design was used, the inoculation amount of Fusarium graminearum was 1×10⁵, 1×10⁶, 1×10⁷ conidia/g, the corn moisture was 22%, cultured in a Erlenmeyer flask, and the oxygen flux was 1020 m²/m³. The temperature was 25±2℃, the humidity was 75%±5%, and the culture time was 60 d. The quality index and two toxins content in corn culture on different culture time were measured.[Results] The amino acid content had a quadratic curve variation (P<0.01), the content of crude fat, starch and crude fiber decreased linearly (P<0.01), the acid value increased linearly (P<0.01), the protein solubility and energy decreased linearly (P<0.01), the mold counting and content of deoxynivalenol, 15-acetyldeoxynivalenol showed a quadratic curve variation (P<0.01). The accumulation dynamic of deoxynivalenol was that the toxin production ranged from 0.17 to 0.23 mg/kg between 0-15 d, from 0.14 to 0.41 mg/kg between 16-20 d, from 0.06 to 0.15 mg/kg between 21-60 d. The accumulation dynamic of 15-acetyldeoxynivalenol was that the toxin production ranged from 1.11 to 5.28 mg/kg between 0 to 5 d, from 5.55 to 10.05 mg/kg between 6-15 d, from 4.68 to 12.06 mg/kg between 16-60 d.[Conclusion] The corn quality decreased gradually with the increase of Fusarium graminearum inoculation amount and culture time. There was a dose-dependent relationship between content of deoxynivalenol, 15-acetyldeoxynivalenol and Fusarium graminearum inoculation amount. The accumulation dynamic of two toxins was found within 60 days.

Abstract:[Objective] In order to find strains suitable for the development of biocontrol agents and biophosphate fertilizer, bacteria with high phosphorus-dissolving efficiency were isolated from the rhizosphere soils of different crops planted in the cold region of north China.[Methods] A highly effective phosphorous-dissolving bacterium was obtained from 26 bacterial strains with phosphorous-dissolving activity through preliminary and second screening. The bacterial strain was identified through physiological, biochemical and molecular biological methods, and its phosphorus-dissolving activity was tested by molybdenum blue colorimetry method. Meanwhile, the antagonism activity to several plant pathogens was determined by plate confrontation method.[Results] Strain B51-7 was obtained by the screening and identified as Burkholderia sp.. The soluble phosphorus content of the strain B51-7 in the fermentation broth reached 832.7 mg/L. Meanwhile, this strain had a broad-spectrum antifungal activity with the highest antagonism rate of 89.71%. A pot experiment showed that the growth of rice was significantly promoted by inoculation of strain B51-7.[Conclusion] Strain B51-7 was a highly effective phosphate-dissolving bacterium with biological control effect, and could be applied for making biological fertilizers and biocontrol agents.

Abstract:The type VI secretion system (T6SS) was an important secretory system found in most Gram-negative bacteria. It mediates the interaction between bacteria and bacteria and between bacteria and host cells. Haemolysin co-regulatory protein (Hcp) and valine glycine repeat protein G (VgrG) were important components of the T6SS puncturing device. However, the role of Hcp and VgrG of the Salmonella typhimurium type VI secretion system in the process of invading host cells and anti-phagocytosis is not completely clear.[Objective] The aim of this study was to inoculate eukaryotic epithelial cells and macrophages in vitro using the hcp and vgrg gene deletion strains constructed by gene knockout technology, and to use their parental strains as a control group, to study the role of Hcp and VgrG genes in the process of adhesioning and invading epithelial cell and anti-phagocytosis.[Methods] We optimized the conditions in the operation of Red homologous recombination system, and established an operating system that rapidly knockout genes related to the type VI secretion system of Salmonella typhimurium, and successfully constructed CVCC541 single deletion strain, double deletion strain, and triple deletion strain, and Hela cell inoculation test and colony count test were used to evaluate the adhesion and invasion ability of different strains; the macrophage RAW 264.7 inoculation test was used to evaluate the anti-phagocytic ability of different strains.[Results] Compared with the CVCC541 strain, the adhesion rates of CVCC541Δvgrg, CVCC541Δhcp2Δvgrg, and CVCC541Δhcp1Δhcp2Δhc3 were 16.17%±2.1%, 14.73%±2.5% and 82%±3.7%, respectively; the invasive rates of CVCC541Δvgrg, CVCC541Δhcp2Δvgrg, and CVCC541Δhcp1Δhcp2Δhcp3 were 7.05%±1.05%, 6.21%±1.35% and 87%±3.25%, respectively. The survival rates of CVCC541Δvgrg, CVCC541Δhcp2Δvgrg and CVCC541Δhcp1Δhcp2Δhcp3 were 15.67%±2.9%, 14.47%±1.87% and 56.12%±3.48%, respectively.[Conclusion] Salmonella typhimurium type VI secretion system VgrG and Hcp played an important role in the process invasioning host cells and anti-phagocytosis. This work created the conditions for the research mechanism of interaction between Salmonella typhimurium and host cells through type VI secretion system secretory system.

Abstract:[Objective] The present study aims to reveal non-Saccharomyces yeasts biodiversity and theirs changes during natural fermentation of Rosa roxburghii fruit, so as to provide reference for the screening of high quality non-Saccharomyces yeasts.[Methods] The composition and biodiversity in non-Saccharomyces yeasts communities in four natural fermentation stages including 1 d (F1), 3 d (F3), 5 d (F5) and 15 d (F15) and the cultures from R. roxburghii in YPD medium were analyzed using high-throughput sequencing and WL (Wallerstein laboratory nutrient agar) identification medium.[Results] High-throughput sequencing results show that a total of 182 operational taxonomic units (OTUs) were detected and assigned to 81 species in 107 genera. Hanseniaspora sp. and Hyphopichia burtonii were predominant in R. roxburghii fruit, accounting for 42.59% and 26.85% in F1, respectively. With the continuous progress of natural fermentation, the content of Hanseniaspora sp. and H. burtonii decreased gradually. At the end of fermentation (F15), the proportion of Hanseniaspora sp. and H. burtonii decreased to 7.73% and 0.52%, respectively. In contrast, the proportion of Pichia sporocuriosa and unclassified_o_Saccharomycetales increased from 0.23%, 0.33% in F1 to 37.26%, 32.62% in F15, respectively. Moreover, Hanseniaspora_sp., H. burtonii, Pichia kluyveri, P. sporocuriosa and Wickerhamomyces anomalus were also isolated by pure culture approach.[Conclusion] There were abundant resources of non-Saccharomyces yeasts in R. roxburghii fruit. Study on the biodiversity of non-Saccharomyces yeasts during natural fermentation of R. roxburghii, it aims to lay a foundation for the exploitation and utilization of these yeast resources.

Abstract:[Objective] This study aims to obtain the miRNAs gene expression profiling of 3D4/21 cells infected with porcine circovirus type 2 (PCV2) and to explore the role of miRNA-98 in the replication of PCV2.[Methods] We used the porcine alveolar macrophage cell lines, 3D4/21 cells, as a cell model to analyze the different miRNAs of 3D4/21 cells infected or uninfected with PCV2. Combined with the results of bioinformatics and experiments, we screened the specific miRNAs related to virus replication and studied the role of miRNA-98 in PCV2 replication.[Results] Differential expression of miRNAs in the process of PCV2 infection was got by high-throughput sequencing technology and evaluated by qRT-RCR and preliminary study. The expression of miRNA-98 increased with the prolongation of PCV2 infection time, and the change trend of miRNA-98 was basically same as that of cap protein of PCV2. These results indicated that a significantly positive correlation between miRNA-98 expression and PCV2 replication. Overexpression of miRNA-98 significantly enhanced PCV2 replication and the expression of Cap. Further evidence supports a link between infection and the host immune regulatory cytokines, which is regulated by miRNA-98.[Conclusion] Overall, miRNA-98 can help PCV2 escape from immune surveillance by regulating the host immune system and enhance PCV2 replication. These results not only supply new insights about relationship between PCV2 infection and host but also provide a potential target for antiviral therapy against PCVAD (porcine circovirus-associated diseases).

Abstract:[Objective] The aim of this study was to evaluate the effects of Macleaya cordata extracts (MCE) instead of antibiotics on growth performance, caecum microbes, short chain fatty acids (SCFAs) and tight junction mRNA expression in yellow-feathered broilers.[Methods] A total of 300 one-day-old Wenshi new yellow broilers No. 2 with similar body weight were randomly allotted to 5 groups, with 6 replicates and 10 broilers per replicate. Broilers in control group were fed a basal diet (NC) and broilers in antibiotic group (ANT), fed a basal diet with 50 mg/kg Nosiheptide and 50 mg/kg chlortetracycline, while those in the treatment groups were fed a basal diet supplemented with 200, 400 and 800 mg/kg MCE. The experiment was lasted for 60 days.[Results] The addition of 400 mg/kg MCE to replace antibiotic growth promoter in yellow-feathered broilers diet significantly reduced (P<0.05) the feed conversion ratio, and significantly increased (P<0.05) the length of the cecum. Dietary supplementation with MCE significantly increased (P<0.05) the cecal Firmicutes and Clostridium cluster XIVa counts and significantly decreased (P<0.05) the Escherichia coli counts. Supplemented with 400 and 800 mg/kg MCE to replace AGPs significantly increased (P<0.05) the cecal total short-chain fatty acids, acetic acid and butyric acid, and 400 mg/kg MCE significantly increased the branched-chain fatty acids, including isobutyrate and isovalerate (P<0.05). Supplementation with MCE in no AGPs diet significantly increased the expression of Claudin-1, JAM2 and ZO-1 (P<0.05). And MCE instead of AGPs significantly increased the expression of JAM2 (P<0.05). However, the addition of MCE to the diet significantly reduced the gene expression of MUC2, MUC5ac and MUC13 (P<0.05).[Conclusion] The MCE replace dietary AGPs of yellow-feathered broilers improves the growth performance promotes caecum growth, and help to establish a stable and healthy intestinal barrier which through increasing the number of beneficial bacteria, SCFAs concentration and regulate the expression of tight junction proteins expression. The optimal addition amount of MCE under this experiment is 400 mg/kg.

Abstract:[Objective] Cofactor lipoic acid participates in many basic cellular metabolic processes. Xanthomonas campestris pv. campestris (Xcc) is the pathogen of black rot of cruciferous plants, causing plant disease all over the world. Studies on the synthetic mechanism of lipoic acid in Xcc will facilitate the discovery of novel methods to control the disease.[Methods] XC_0713 (XccLipA) and XC_0712 (XccLipB) in Xcc were found based on the sequence alignments with E. coli LipA and LipB, the key enzymes for lipoic acid synthesis. For complementation analysis, XcclipA and XcclipB were amplified and ligated into expression vector pBAD24M, which were further transferred into E. coli mutants, respectively. The growth of transformants was analyzed. With the aid of E. coli lplA expression, XcclipA and XcclipB were deleted in the genome by homologous recombination, respectively. The growth and virulence of the two mutants were analyzed.[Results] XcclipA and XcclipB complemented the growth of E.coli fabA and fabB mutants on the minimal media, respectively. Both XcclipA and XcclipB are essential genes, which cannot be deleted directly. However, XcclipA and XcclipB could be deleted when pSRK-EclplA was introduced. The two mutants could not grow on the minimal medium, but grew well when lipoic acid supplemented. XcclipB mutant could grow on the nutritional medium. XcclipA mutant almost abolished the virulence to the host plant, but XcclipB mutant showed similar virulence with wild-type strain.[Conclusion] XcclipA codes lipoyl synthase, and XcclipB codes octanoyl transferrase, both are essential genes for Xcc growth. The LipB-LipA is the only lipoic acylation pathway in Xcc. XcclipA deletion mutant showed no virulence to host plant, indicating XccLipA is a promising target for anti-bacteria agent selection.